package cn.featherfly.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Locale;

/**
 * Defines an object to assist a servlet in sending a response to the client. The servlet container
 * creates a
 * <code>ServletResponse</code> object and passes it as an argument to the servlet's
 * <code>service</code> method.
 * <p>
 * To send binary data in a MIME body response, use the {@link ServletOutputStream} returned by
 * {@link #getOutputStream}. To send character data, use the <code>PrintWriter</code> object
 * returned by
 * {@link #getWriter}. To mix binary and text data, for example, to create a multipart response, use
 * a
 * <code>ServletOutputStream</code> and manage the character sections manually.
 * <p>
 * The charset for the MIME body response can be specified explicitly using any of the following
 * techniques: per
 * request, per web-app (using {@link ServletContext#setRequestCharacterEncoding}, deployment
 * descriptor), and per
 * container (for all web applications deployed in that container, using vendor specific
 * configuration). If multiple of
 * the preceding techniques have been employed, the priority is the order listed. For per request,
 * the charset for the
 * response can be specified explicitly using the {@link #setCharacterEncoding(String)},
 * {@link #setCharacterEncoding(Charset)} and {@link #setContentType} methods, or implicitly using
 * the
 * {@link #setLocale} method. Explicit specifications take precedence over implicit specifications.
 * If no charset is
 * explicitly specified, ISO-8859-1 will be used. The <code>setCharacterEncoding</code>,
 * <code>setContentType</code>, or
 * <code>setLocale</code> method must be called before <code>getWriter</code> and before committing
 * the response for the
 * character encoding to be used.
 * <p>
 * See the Internet RFCs such as <a href="http://www.ietf.org/rfc/rfc2045.txt"> RFC 2045</a> for
 * more information on
 * MIME. Protocols such as SMTP and HTTP define profiles of MIME, and those standards are still
 * evolving.
 *
 * @author Various
 * @see ServletOutputStream
 */
public interface ServletResponse {

    /**
     * Returns the name of the character encoding (MIME charset) used for the body sent in this
     * response. The following
     * methods for specifying the response character encoding are consulted, in decreasing order of
     * priority: per request,
     * perweb-app (using {@link ServletContext#setResponseCharacterEncoding}, deployment
     * descriptor), and per container (for
     * all web applications deployed in that container, using vendor specific configuration). The
     * first one of these methods
     * that yields a result is returned. Per-request, the charset for the response can be specified
     * explicitly using the
     * {@link #setCharacterEncoding(String)}, {@link #setCharacterEncoding(Charset)} and
     * {@link #setContentType} methods, or
     * implicitly using the setLocale(java.util.Locale) method. Explicit specifications take
     * precedence over implicit
     * specifications. Calls made to these methods after <code>getWriter</code> has been called or
     * after the response has
     * been committed have no effect on the character encoding. If no character encoding has been
     * specified,
     * <code>ISO-8859-1</code> is returned.
     * <p>
     * See RFC 2047 (http://www.ietf.org/rfc/rfc2047.txt) for more information about character
     * encoding and MIME.
     *
     * @return a <code>String</code> specifying the name of the character encoding, for example,
     *         <code>UTF-8</code>
     */
    String getCharacterEncoding();

    /**
     * Returns the content type used for the MIME body sent in this response. The content type
     * proper must have been
     * specified using {@link #setContentType} before the response is committed. If no content type
     * has been specified, this
     * method returns null. If a content type has been specified, and a character encoding has been
     * explicitly or implicitly
     * specified as described in {@link #getCharacterEncoding} or {@link #getWriter} has been
     * called, the charset parameter
     * is included in the string returned. If no character encoding has been specified, the charset
     * parameter is omitted.
     *
     * @return a <code>String</code> specifying the content type, for example,
     *         <code>text/html; charset=UTF-8</code>, or
     *         null
     * @since Servlet 2.4
     */
    String getContentType();

    //    /**
    //     * Returns a {@link ServletOutputStream} suitable for writing binary data in the response. The
    //     * servlet container does
    //     * not encode the binary data.
    //     * <p>
    //     * Calling flush() on the ServletOutputStream commits the response.
    //     * Either this method or {@link #getWriter} may be called to write the body, not both, except
    //     * when {@link #reset} has
    //     * been called.
    //     *
    //     * @return a {@link ServletOutputStream} for writing binary data
    //     * @exception IllegalStateException if the <code>getWriter</code> method has been called on this
    //     *            response
    //     * @exception IOException if an input or output exception occurred
    //     * @see #getWriter
    //     * @see #reset
    //     */
    //    ServletOutputStream getOutputStream() throws IOException;

    /**
     * Returns a <code>PrintWriter</code> object that can send character text to the client. The
     * <code>PrintWriter</code>
     * uses the character encoding returned by {@link #getCharacterEncoding}. If the response's
     * character encoding has not
     * been specified as described in <code>getCharacterEncoding</code> (i.e., the method just
     * returns the default value
     * <code>ISO-8859-1</code>), <code>getWriter</code> updates it to <code>ISO-8859-1</code>.
     * <p>
     * Calling flush() on the <code>PrintWriter</code> commits the response.
     * <p>
     * Either this method or {@link #getOutputStream} may be called to write the body, not both,
     * except when {@link #reset}
     * has been called.
     *
     * @return a <code>PrintWriter</code> object that can return character data to the client
     * @exception java.io.UnsupportedEncodingException if the character encoding returned by
     *            <code>getCharacterEncoding</code> cannot be used
     * @exception IllegalStateException if the <code>getOutputStream</code> method has already been
     *            called for this response
     *            object
     * @exception IOException if an input or output exception occurred
     * @see #getOutputStream
     * @see #setCharacterEncoding
     * @see #reset
     */
    PrintWriter getWriter() throws IOException;

    /**
     * Sets the character encoding (MIME charset) of the response being sent to the client, for
     * example, to UTF-8. If the
     * response character encoding has already been set by
     * {@link ServletContext#setResponseCharacterEncoding}, the
     * deployment descriptor, or using the {@link #setCharacterEncoding(Charset)},
     * {@link #setContentType} or
     * {@link #setLocale} methods, the value set in this method overrides all of those values.
     * Calling
     * {@link #setContentType} with the <code>String</code> of <code>text/html</code> and calling
     * this method with the
     * <code>String</code> of <code>UTF-8</code> is equivalent to calling {@link #setContentType}
     * with the
     * <code>String</code> of <code>text/html; charset=UTF-8</code>.
     * <p>
     * This method can be called repeatedly to change the character encoding. This method has no
     * effect if it is called
     * after <code>getWriter</code> has been called or after the response has been committed.
     * <p>
     * If calling this method has an effect (as per the previous paragraph), calling this method
     * with {@code null} clears
     * any character encoding set via a previous call to this method,
     * {@link #setCharacterEncoding(Charset)},
     * {@link #setContentType} or {@link #setLocale} but does not affect any default character
     * encoding configured via
     * {@link ServletContext#setResponseCharacterEncoding} or the deployment descriptor.
     * <p>
     * If this method is called with an invalid or unrecognised character encoding, then a
     * subsequent call to
     * {@link #getWriter()} will throw a {@link UnsupportedEncodingException}. Content for an
     * unknown encoding can be sent
     * with the {@link ServletOutputStream} returned from {@link #getOutputStream()}.
     * <p>
     * Containers may choose to log calls to this method that use an invalid or unrecognised
     * character encoding.
     * <p>
     * Containers must communicate the character encoding used for the servlet response's writer to
     * the client if the
     * protocol provides a way for doing so. In the case of HTTP, the character encoding is
     * communicated as part of the
     * <code>Content-Type</code> header for text media types. Note that the character encoding
     * cannot be communicated via
     * HTTP headers if the servlet does not specify a content type; however, it is still used to
     * encode text written via the
     * servlet response's writer.
     *
     * @param encoding a String specifying only the character set defined by IANA Character Sets
     *        (http://www.iana.org/assignments/character-sets) or {@code null}
     * @see #setCharacterEncoding(Charset)
     * @see #setContentType
     * @see #setLocale
     * @since Servlet 2.4
     */
    void setCharacterEncoding(String encoding);

    /**
     * Sets the character encoding (MIME charset) of the response being sent to the client, for
     * example, to UTF-8. If the
     * response character encoding has already been set by
     * {@link ServletContext#setResponseCharacterEncoding}, the
     * deployment descriptor, or using the {@link #setCharacterEncoding(String)},
     * {@link #setContentType} or
     * {@link #setLocale} methods, the value set in this method overrides all of those values.
     * Calling
     * {@link #setContentType} with the <code>String</code> of <code>text/html</code> and calling
     * this method with
     * {@link StandardCharsets#UTF_8} is equivalent to calling {@link #setContentType} with the
     * <code>String</code> of
     * <code>text/html; charset=UTF-8</code>.
     * <p>
     * This method can be called repeatedly to change the character encoding. This method has no
     * effect if it is called
     * after <code>getWriter</code> has been called or after the response has been committed.
     * <p>
     * If calling this method has an effect (as per the previous paragraph), calling this method
     * with {@code null} clears
     * any character encoding set via a previous call to this method,
     * {@link #setCharacterEncoding(String)},
     * {@link #setContentType} or {@link #setLocale} but does not affect any default character
     * encoding configured via
     * {@link ServletContext#setResponseCharacterEncoding} or the deployment descriptor.
     * <p>
     * Containers must communicate the character encoding used for the servlet response's writer to
     * the client if the
     * protocol provides a way for doing so. In the case of HTTP, the character encoding is
     * communicated as part of the
     * <code>Content-Type</code> header for text media types. Note that the character encoding
     * cannot be communicated via
     * HTTP headers if the servlet does not specify a content type; however, it is still used to
     * encode text written via the
     * servlet response's writer.
     * <p>
     * Implementations are strongly encouraged to override this default method and provide a more
     * efficient implementation.
     *
     * @param encoding a Charset instance representing the encoding to use or {@code null}
     * @see #setCharacterEncoding(String)
     * @see #setContentType
     * @see #setLocale
     * @since Servlet 6.1
     */
    default void setCharacterEncoding(Charset encoding) {
        setCharacterEncoding(encoding.name());
    }

    /**
     * Sets the length of the content body in the response In HTTP servlets, this method sets the
     * HTTP Content-Length
     * header.
     * <p>
     * This method may be called repeatedly to change the content length. This method has no effect
     * if called after the
     * response has been committed.
     *
     * @param len an integer specifying the length of the content being returned to the client; sets
     *        the Content-Length
     *        header
     */
    void setContentLength(int len);

    /**
     * Sets the length of the content body in the response In HTTP servlets, this method sets the
     * HTTP Content-Length
     * header.
     * <p>
     * This method may be called repeatedly to change the content length. This method has no effect
     * if called after the
     * response has been committed.
     *
     * @param len a long specifying the length of the content being returned to the client; sets the
     *        Content-Length header
     * @since Servlet 3.1
     */
    void setContentLengthLong(long len);

    /**
     * Sets the content type of the response being sent to the client, if the response has not been
     * committed yet. The given
     * content type may include a character encoding specification, for example,
     * <code>text/html;charset=UTF-8</code>. The
     * response's character encoding is only set from the given content type if this method is
     * called before
     * {@link #getWriter()} is called.
     * <p>
     * This method may be called repeatedly to change content type and character encoding. This
     * method has no effect if
     * called after the response has been committed. It does not set the response's character
     * encoding if it is called after
     * <code>getWriter</code> has been called or after the response has been committed.
     * <p>
     * If calling this method has an effect (as per the previous paragraph), calling this method
     * with {@code null} clears
     * any content type set via a previous call to this method and clears any character encoding set
     * via a previous call to
     * this method, {@link #setCharacterEncoding(String)}, {@link #setCharacterEncoding(Charset)} or
     * {@link #setLocale} but
     * does not affect any default character encoding configured via
     * {@link ServletContext#setResponseCharacterEncoding} or
     * the deployment descriptor.
     * <p>
     * If this method is called with an invalid or unrecognised character encoding, then a
     * subsequent call to
     * {@link #getWriter()} will throw a {@link UnsupportedEncodingException}. Content for an
     * unknown encoding can be sent
     * with the {@link ServletOutputStream} returned from {@link #getOutputStream()}.
     * <p>
     * Containers may choose to log calls to this method that use an invalid or unrecognised
     * character encoding.
     * <p>
     * Containers must communicate the content type and the character encoding used for the servlet
     * response's writer to the
     * client if the protocol provides a way for doing so. In the case of HTTP, the
     * <code>Content-Type</code> header is
     * used.
     *
     * @param type a <code>String</code> specifying the MIME type of the content or {@code null}
     * @see #setLocale
     * @see #setCharacterEncoding(String)
     * @see #setCharacterEncoding(Charset)
     * @see #getOutputStream
     * @see #getWriter
     */
    void setContentType(String type);

    /**
     * Sets the preferred buffer size for the body of the response. The servlet container will use a
     * buffer at least as
     * large as the size requested. The actual buffer size used can be found using
     * <code>getBufferSize</code>.
     * <p>
     * A larger buffer allows more content to be written before anything is actually sent, thus
     * providing the servlet with
     * more time to set appropriate status codes and headers. A smaller buffer decreases server
     * memory load and allows the
     * client to start receiving data more quickly.
     * <p>
     * This method must be called before any response body content is written; if content has been
     * written or the response
     * object has been committed, this method throws an <code>IllegalStateException</code>.
     *
     * @param size the preferred buffer size
     * @exception IllegalStateException if this method is called after content has been written
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     * @see #reset
     */
    void setBufferSize(int size);

    /**
     * Returns the actual buffer size used for the response. If no buffering is used, this method
     * returns 0.
     *
     * @return the actual buffer size used
     * @see #setBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     * @see #reset
     */
    int getBufferSize();

    /**
     * Forces any content in the buffer to be written to the client. A call to this method
     * automatically commits the
     * response, meaning the status code and headers will be written.
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     * @throws IOException if the act of flushing the buffer cannot be completed.
     */
    void flushBuffer() throws IOException;

    /**
     * Clears the content of the underlying buffer in the response without clearing headers or
     * status code. If the response
     * has been committed, this method throws an <code>IllegalStateException</code>.
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     * @since Servlet 2.3
     */
    void resetBuffer();

    /**
     * Returns a boolean indicating if the response has been committed. A committed response has
     * already had its status code
     * and headers written.
     *
     * @return a boolean indicating if the response has been committed
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #reset
     */
    boolean isCommitted();

    /**
     * Clears any data that exists in the buffer as well as the status code, headers. The state of
     * calling
     * {@link #getWriter} or {@link #getOutputStream} is also cleared. It is legal, for instance, to
     * call
     * {@link #getWriter}, {@link #reset} and then {@link #getOutputStream}. If {@link #getWriter}
     * or
     * {@link #getOutputStream} have been called before this method, then the corrresponding
     * returned Writer or OutputStream
     * will be staled and the behavior of using the stale object is undefined. If the response has
     * been committed, this
     * method throws an <code>IllegalStateException</code>.
     *
     * @exception IllegalStateException if the response has already been committed
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     */
    void reset();

    /**
     * Sets the locale of the response, if the response has not been committed yet. It also sets the
     * response's character
     * encoding appropriately for the locale, if the character encoding has not been explicitly set
     * using
     * {@link #setContentType}, {@link #setCharacterEncoding(String)} or
     * {@link #setCharacterEncoding(Charset)},
     * <code>getWriter</code> hasn't been called yet, and the response hasn't been committed yet. If
     * the deployment
     * descriptor contains a <code>locale-encoding-mapping-list</code> element, and that element
     * provides a mapping for the
     * given locale, that mapping is used. Otherwise, the mapping from locale to character encoding
     * is container dependent.
     * <p>
     * This method may be called repeatedly to change locale and character encoding. The method has
     * no effect if called
     * after the response has been committed. It does not set the response's character encoding if
     * it is called after
     * {@link #setContentType} has been called with a charset specification, after
     * {@link #setCharacterEncoding(String)} has
     * been called, after {@link #setCharacterEncoding(Charset)} has been called, after
     * <code>getWriter</code> has been
     * called, or after the response has been committed.
     * <p>
     * If calling this method has an effect on the locale (as per the previous paragraph), calling
     * this method with
     * {@code null} clears any locale set via a previous call to this method. If calling this method
     * has an effect on the
     * character encoding, calling this method with {@code null} clears the previously set character
     * encoding.
     * <p>
     * Containers must communicate the locale and the character encoding used for the servlet
     * response's writer to the
     * client if the protocol provides a way for doing so. In the case of HTTP, the locale is
     * communicated via the
     * <code>Content-Language</code> header, the character encoding as part of the
     * <code>Content-Type</code> header for text
     * media types. Note that the character encoding cannot be communicated via HTTP headers if the
     * servlet does not specify
     * a content type; however, it is still used to encode text written via the servlet response's
     * writer.
     *
     * @param loc the locale of the response or {code @null}
     * @see #getLocale
     * @see #setContentType
     * @see #setCharacterEncoding(String)
     * @see #setCharacterEncoding(Charset)
     */
    void setLocale(Locale loc);

    /**
     * Returns the locale specified for this response using the {@link #setLocale} method. Calls
     * made to
     * <code>setLocale</code> after the response is committed have no effect. If no locale has been
     * specified, the
     * container's default locale is returned.
     *
     * @return the Locale for this response.
     * @see #setLocale
     */
    Locale getLocale();

}
